The present invention relates to a yoke for universal joint including a base portion and a pair of opposed side walls which extend from the base portion so as to face each other at a distance. In the yoke, one end of a rotating shaft inserted between the opposed side walls is interposed and fixed by the base portion and the opposed side walls when fastening portions of the opposed side walls at the leading ends thereof are fastened by a fastener.
A universal joint 100 serves to connect two shafts, of which the shaft lines intersect at a certain angle, so as to transmit the torque of one shaft to the other shaft. As shown in FIG. 8, the universal joint 100 includes a cross joint 101, of which the shaft lines cross each other, and two yokes 102 and 103 (a first yoke 102 and a second yoke 103), which are respectively connected to both ends of the shafts composing the joint cross 101 so as to rock around the shaft lines and to which one ends of rotating shafts 111 and 112 are respectively connected. The universal joint 100 is provided in a steering device of a vehicle, for example (refer to JP-A-10-9281).
The steering device transmits the torque of a steering shaft 111 to an input shaft 112 of a steering gear through the universal joint 100, and the steering shaft 111 is rotated by the manipulation of steering wheel, so that the steering device imparts a steering angle to a front wheel.
The first yoke 102 includes a base portion 102a and a pair of opposed side walls 102b which extend from the base portion 102a so as to face each other at a distance. One end of the steering shaft 111 is fixed to the outer surface of the base portion 102a, and the joint cross 101 is attached on the inner surfaces of the opposed side walls 102b at the leading ends thereof.
As shown in FIGS. 8 to 10, the second yoke 103 includes a base portion 103a and a pair of opposed side walls 103b which extend from the base portion 103a so as to face each other at a distance, similar to the first yoke 102. The base portion 103a is formed only in a base part of the opposed side walls 103b at one end, and the respective opposed side walls 103b are formed so that the space between the opposed side walls 103b is widened from the base part to the leading end, as shown by a chain double-dashed line of FIG. 10. Further, in the respective opposed side walls 103b, an attachment hole 103c to which the joint cross 101 is attached is formed in the other end thereof, and a through-hole 103d is formed in the one end and the leading end thereof.
One end of the input shaft 112 of the steering gear is connected to the second yoke 103. Specifically, one end of the input shaft 112 is inserted between the opposed side walls 103b such that the second yoke 103 rocks around the axis line of the joint cross 101, and the outer periphery of the input shaft 112 is abutted on the inner surface of the base portion 103a. Then, when the leading ends of the opposed side walls are fastened by a bolt 113 having an eccentric shaft 113a and a nut 114, the input shaft 112 is interposed by the base portion 103a and the opposed side walls 103b, and the outer periphery of the input shaft 112 opposite to the base portion 103a (the bottom surface of a notched portion 112a to be described) is pressed by the eccentric shaft 113a of the bolt 113. Accordingly, the second yoke 103 and the input shaft 112 are coupled and fixed to each other.
The one end of the input shaft 112 is formed on a plane such that the opposing surfaces (two planes) with respect to the opposed side walls 103b are parallel to each other. On the surface of the input shaft 112 opposite to the base portion 103a, a notched portion 112a is formed so as to avoid the interference with the bolt 113 and to prevent the input shaft 112 from coming off from the second yoke 103 when the input shaft 112 moves in the shaft line direction. Further, the intersection portion between the bottom surface of the notched portion 112a and the surface opposed to the side wall 10b is formed in a square shape (square corner).
Patent Document 1: JP-A-10-9281
However, although the input shaft 112 is pushed against the inner surface of the base portion 103a by the eccentric shaft 113a of the bolt 113 in the coupling between the second yoke 103 and the input shaft 112 of the steering gear, a deviation into the rotation direction centered on the pressed portion of the input shaft 112 by the bolt 113 or a deviation into the axial direction of the input shaft 112 (refer to a direction of an arrow of FIG. 9) occurs between the second yoke 103 and the input shaft 112 due to an external force or vibration acting on the second yoke 103 and the input shaft 112. Such a deviation results in noise and makes the transmission of torque incomplete.